Electronic fuel injectors are frequently used in today's internal combustion engines. The electronic fuel injector provides precise and reliable fuel delivery into the cylinder of compression ignition and spark ignition engines. The precision and reliability of the electronic fuel injector have contributed to the goals of fuel efficiency, maximum practicable power output and control of undesirable products of combustion. These and other benefits of electronic fuel injection systems are well known and are appropriately used to beneficial effect in the design of modern internal combustion engines.
Known electronic fuel injectors, especially those designed for application in spark ignition or compression ignition engines, utilize means to enhance fuel charge pressurization. Enhanced fuel charge pressurization is desirable during the fuel injection event to assure proper atomization and spray distribution of the fuel into the engine cylinder or prechamber. In addition, it is desirable to be able to determine the quantity of fuel used and to control the injection timing for several reasons, including obtaining full combustion of the fuel to control particulate emissions. This has been of great interest in recent years, owing to environment concerns and regulatory incentives. Finally, the proper control of fuel injectors reduces the amount of residual particulate formed in the compression ignition engine cylinder.
Several known types of fuel injectors include a means which enhances the pressurization of the fuel charge. These fuel injectors typically have mechanical linkage systems coupled to the engine camshaft and/or cylinder head valve train assembly. Such fuel injectors are configured so that the camshaft or other rotating or reciprocating member acts on an injector push rod either directly or indirectly through a rocker arm.
The link is generally vertically oriented with respect to the injector. Displacement of the link in the downward direction (along the vertical axis) also causes an injector coupling to move downward within a bore created in the fuel injector body. The coupling is spring loaded and is returned to its original position by the bias force of a coupling return spring. The injector coupling is attached to a timing plunger and movement of the coupling causes relative movement of the timing plunger. When the injection coupling moves downward, the timing plunger moves downward into a timing plunger chamber, which causes a metering plunger to move in a metering plunger chamber which contains a prefilled and measured volume of fuel. The movement of the metering plunger provides additional pressure to the fuel charge in the metering plunger chamber exceeding the pressure of the rail fuel (fuel delivered to the injector from the fuel pump at about 150 psi). This additional pressure, after exceeding a certain pressure threshold, causes an injector nozzle to open and allows the fuel to flow through the injector nozzle into a combustion chamber or equivalent structure at very high pressure. The return stroke of the timing plunger is generally facilitated by the use of the return spring force acting on the attached coupling.
Control of the injection sequence, relative to the timing and volume of the fuel injected into the engine cylinder or equivalent structure, is often accomplished with an electronically actuated control valve. The actuation of the control valve is achieved by means well known in the art, especially including a control solenoid, which is typically situated parallel to the central axis of the injector body due to space limitations existing in the valve train assembly. Passages are machined within the injector body to allow the transportation of fuel at the rail fuel pressure of 150 psi between the control valve operable by the control valve solenoid and the timing plunger chamber during the metering stroke, and allow preinjection backflow to occur during the injection stroke. By selectively opening and closing the control valve via the control solenoid, the amount of fuel flowing through the passages into the injector can be directly or indirectly metered. Due to the often complicated passage formations necessary to allow fuel transportation between the two parallel axis of the control solenoid and the injector body, it is typically necessary to perform drilling and machining operations in the formation of the passages which require access orifices and channels through the exterior surface of the injector body, which are subsequently sealed with high pressure plugs.
Further, in some injector configurations, the amount of fuel to be injected is established by using a timing plunger chamber in series with the axial motion of the injector link, coupling member, timing plunger, metering plunger and metering plunger chamber. The timing plunger chamber is located between the timing plunger and the metering plunger. The timing plunger chamber controls admitting fuel at 150 psi and thus the upward motion of the metering plunger by balancing the fluid pressure acting on both axial ends of the metering plunger. As the injection stroke progresses, pressurization of the timing plunger chamber is avoided by allowing the fuel contained therein to flow back through the control valve passage and control valve. Thus, the control solenoid can be used to control preinjection back flow from the timing plunger chamber back through the injector body passages and the control valve to the fuel rail. This function has the beneficial result of maintaining a constant pressure in the timing plunger chamber and maintaining the proper volume of metered fuel already delivered to the metering chamber.
As the injection sequence continues, the control valve is closed, thus preventing further preinjection backflow. Accordingly, the fuel present in the timing plunger chamber and the metering plunger chamber is subject to increasing pressure as the timing plunger continues and the metering plunger begins their downward travel in the injector body.
The control valve and associated passages in the injector body are fully exposed to the pressurization of the fuel in both the timing plunger chamber and metering chamber throughout the final high pressure phase of the injection stroke. Although the fuel is introduced into the fuel injector at about 150 psi, the peak pressure of the fuel during the injection phase reaches transient pressures of 23,500 psi. These pressures are also exerted against the high pressure plugs used to seal the passages from the exterior of the injector body.
In the fuel injector in common use several years ago the injection pressures were only in the range of 10,000 to 12,000 psi. These pressures did not significantly contribute to plug failures, as these pressures were typically far below the performance limits of the plugs. The higher injection pressures present in modern engines for the reasons noted above are contributing to the increased occurrence of plug failures, as these higher pressures are approaching, if not exceeding, the performance limits of the plugs.
Failure of the plug during engine operation can result in serious damage to the engine. The fuel provided to the injector at fuel rail pressures can escape from the confines of the injector body and flow into the cylinder head. There, the fuel can mix with the engine lubricant and compromise the integrity of the engine lubricant throughout the engine. The use of the diluted engine lubricant with impaired performance characteristics can cause severe and catastrophic failures of key engine sliding surfaces, such as the engine main bearings.